1. Field of the Invention
This invention relates to improved transfer gates for transferring magnetic bubble domains selectively between different propagation paths, and more particularly to an improved transfer gate using a magnetic charged wall which bridges the propagation
2. Description of the Prior Art
In the magnetic bubble domain art, it is known to use ion implantation to produce contiguous propagation elements along which magnetic bubble domains move as a magnetic field reorients in the plane of the magnetic medium. Such a technique is shown in U.S. Pat. No. 3,828,329. Further work with high density contiguous structures (such as discs) and particularly techniques for producing such structures are shown in U.S. Pat. No. 3,967,002, which is assigned to the present assignee. Still another application which describes an improved process for making contiguous disk bubble storage devices is copending application Ser. No. 645,975, filed Dec. 31, 1975 and now abandoned, in the name of G. E. Keefe, and also assigned to the present assignee. This copending application is specifically directed to a technique for making submicron contiguous disk devices using ion implanted structures, where only two masking steps are required to make a complete memory.
In most bubble domain memory organizations, and particularly in the well known major/minor loop organization, a transfer switch is required for transferring bubble domains from one propagation path to another. Where contiguous propagation elements are used for the major and minor loops, the transfer switch is typically a wide conductor bridging the major loop propagation path and the various minor loop propagation paths. However, wide conductors, and other types of transfer gates, do not have transfer margins which are as great as the margins obtained for bubble propagation along a shift register. Since the operating margin of the complete memory depends upon the operating margins of its individual components, the transfer gate operation is a very critical one.
The wide conductor transfer gates known in the art carry current which provides a gradient field that is used to switch the bubble back and forth between the major and minor loops. The major loop propagation path is separated sufficiently far from the minor loop propagation paths so that independent propagation can be obtained in each of them. For this reason, the transfer conductor is generally wider than that which is dictated by the high density lithography limitations in the memory. This means that the absolute value of the magnetic field produced by current in the wide conductor at the edges of the conductor is often larger than the gradient field required to move bubble domains. Consequently, the bias field margin which the bubbles can tolerate is lessened due to the rather large magnetic fields produced at the edge of this conductor when current passes through it. These fields are often large enough to collapse the bubble before it could be moved by the gradient field of the conductor.
In order to overcome the disadvantages associated with prior art transfer switches, and particularly those used to transfer bubble domains between major and minor loops in a high density, contiguous element structure, an improved transfer switch has been designed. This improved transfer switch does not use a conductor or a magnetic overlay element to provide the major translational force for the bubble transfer operation. Rather, a magnetic charged wall is used as the primary driving force, and current through an associated conductor is used merely to modify the intensity of the magnetic charged wall. In this manner, the operating margin of the transfer switch is improved and the switching currents exhibit reduced amplitudes. As will be more fully apparent, the transfer switches of the present application utilize the physics of magnetic bubble technology in a natural way in order to provide a transfer switch which operates effectively without stringent lithography requirements.
Accordingly, it is a primary object of the present invention to provide a more efficient transfer switch for moving bubble domains between different propagation paths.
It is another object of the present invention to provide an improved bubble domain transfer switch which requires less current for transfer than previous switches.
It is still another object of this invention to provide an improved transfer switch for transferring bubble domains selectively between different contiguous element propagation paths.
It is a further object of the present invention to provide a transfer switch for moving magnetic bubble domains between selected propagation paths, where the switch utilizes the naturally occurring features of magnetic bubble technology.
It is a still further object of the present invention to provide a switch for transferring bubble domains between two propagation paths where the switch does not require difficult mask alignment to fabricate.
It is another object of the present invention to provide an improved switch for movement of very small magnetic bubble domains between selected propagation paths in high density contiguous element structures.
It is another object of this invention to provide an improved bubble domain transfer switch which is effective over a wide range of orientations of a reorienting magnetic field used to move the bubble domains.